Trotsenko Y. Dynamic characteristics of a fluid flow in variable cross-section ducts

The thesis is devoted to the study of a flow of Newtonian fluid in a cylindrical duct with two serial diaphragms (sharp constrictions of cross-sections). The flow rate is considerably lower than the speed of sound in the medium. The structure of the flow is non-stationary due to the complex geometry of the system. Under certain conditions, this leads to self-sustained oscillations of the medium and in consequence the appearance of tonal sound. The solution of the non-linear boundary value problem was carried out by the direct numerical simulation. The solution algorithm was based on the finite volume method using second-order accurate in both space and time difference schemes. The flow formation process and characteristics of the medium motion in the region between the constrictions were analyzed depending on the Reynolds number, the diameter and length of the cavity formed by the diaphragms, and the shape of the diaphragms. The characteristics and patterns of the occurrence of self-oscillations of a three-dimensional flow were determined. The results obtained for the three-dimensional flow model are compared with the results obtained for the axisymmetric flow model.